1. Field of the Invention
The invention pertains to electrical sockets for use with light bulbs and more particularly to sockets which do not require the use of terminal screws with the bared ends of conductors but use insulation displacing contacts to sever the insulation and displace same to allow electrical contact with the bare metal of the conductors within.
2. Description of the Prior Art
Lamp cord or so called "Zip" cord having two side by side conductors each individually insulated and joined to one another by a web is commonly used for wiring electrical devices, for extension cords and similar devices. One way of using such cord is to strip the insulation from the ends of the conductors and join the conductors to such devices at terminal screws. Another method uses quick wiring techniques on such devices as lamp sockets, switches, taps and receptacles, in which the fully insulated lamp cord is inserted into the device adjacent one or more insulation piercing contacts for each conductor and an actuating device is operated to cause the contacts to pierce the insulation and make electrical contact with the conductors within.
A typical device of this latter arrangement is shown in U.S. Pat. No. 4,874,329 issued Oct. 17, 1989. FIG. 1 of the instant Application is FIG. 3 of the '329 patent. Two sets of saw-tooth shaped insulation piercing contacts 151 and 161 are shown. The electrical cord 17 is inserted into chamber 143' through an opening 144. The actuating device or coupling means 14 is then pushed towards the serrated piercing terminal portions 151 and 161. The width of the piercing terminal portions 151 and 161 are transverse to the strands of wires in the cord 17. These portions 151 and 161 generally sever the wire strands they engage decreasing the number of strands available to conduct current, increasing the current density in the remaining strands and causing the joint to run hotter than it normally would and perhaps cause the joint to burn up. The unsevered strands of wire are held in place against the piercing terminal portions by the insulation above the terminal portions. However, as the insulation ages, hastened by the heat from the joint, the insulation thins, shrinks, hardens, evaporates and creeps permitting the wire strands to move away from the terminal portion further increasing the possibility of joint failure with attendant overheating, smoking, burning and perhaps, fire.
With some of the newer cord insulations using synthetic rubber or plastics or the like there is chance that wide chisel-like terminal portions will merely distort the insulation but not pierce it or drag a portion of the insulation with the terminal portion into the cord making for a poor or no electrical joint with the conductors.
Because of the placement of the serrated piercing terminal portions 151, 161 in the '329 abreast of one another and at the end opposite to the fulcrum of coupling means 14 a great deal of force is required to pierce the cord insulation and because of the lack of lateral support the terminal portions 151, 161 may be deflected sideways entering the insulation but not the wire strands.